Airbag retention systems in the area of the pelvis of a passenger are known. With these known systems, airbags are placed on a lap belt, or a seat belt is formed as an airbag.
Thus, an airbag for seat belts is known from DE 43 06 528 A1 wherein an airbag pocket is fitted onto the existing belt and is connected to a compressed air line as well as to a compressed air generator and release mechanism. The advantage of this belt airbag is that as opposed to airbags that are stored on the steering wheel or on parts of the vehicle body in front of the passenger, this airbag is attached directly to the passenger, i.e., it is located right in the area where it is to exert its protective effect. With this arrangement, the upper part of the body and the head are additionally protected by the airbag. However, the area of the pelvis is as before only restrained by the lap belt. The lap belt's taut fit against the body and the lap belt's small contact surface area against the body can lead to injury in the event of a crash.
Furthermore, an inflatable seat belt unit is known from DE 42 32 041 A1 wherein at least a part of a section that is in contact with a passenger in a vehicle is formed in a bag-like shape. In the inactivated state, the bag-like section retains a belt-like shape. In the event of a crash, the seat belt is inflated and unfolded by gas. With this seat belt unit, the seat belt itself is thus formed in sections as an airbag. The contact bearing face of the seat belt is enlarged through the inflation of the bag-like section so that the strain on the body through the belt in the event of a crash is reduced. An additional protection of the upper body and head cannot however be achieved with this arrangement.